Hydraulic fracturing is an important technique in the oilfield that includes placing or extending channels from the wellbore to the reservoir. This operation includes hydraulically injecting a fracturing fluid into a wellbore penetrating or adjacent to a petroleum-producing subterranean formation and forcing the fracturing fluid against the surrounding subterranean formation by pressure. The subterranean material is forced to crack, creating or enlarging one or more fractures. Proppant can be placed in fractures to prevent or reduce closure. The fractures can provide flow or can provide improved flow of the recoverable fluids from the formation, such as petroleum materials.
Viscous fluids are frequently used during downhole operations. For example, during a pad stage of fracturing, a fluid including viscosifier can be injected to begin to break into an area and initiate fractures to produce sufficient penetration and width to allow proppant-laden later stages to enter. In other examples, during various downhole operations solid materials are formed into a suspension with a viscous fluid and injected downhole. For example, during the slurry phase of hydraulic fracturing operations, a suspension of proppant is formed with fracturing fluid and injected downhole for deposition in fractures. Another example includes gravel pack operations, wherein a suspension of gravel is formed in a viscous fluid for transport downhole. After use of the viscous fluid downhole, a subsequent step usually involves removing from the fracture or other subterranean material to restore permeability and allow produced petroleum or downhole fluids to flow freely through the area. However, the high viscosity of the fluid can make removal difficult.
Viscous fluids for downhole operations are often formed using a gel or crosslinked gel, such as a crosslinked guar or guar derivatives. One technique for removing crosslinked guar includes the use of oxidative or enzymatic breakers. However, oxidative and enzymatic breakers suffer with poor efficiency and failure to provide adequate breakdown of the gel, which can, for example, cause gels to reheal (e.g., increase in viscosity and re-gel) as the temperature drops during extraction, or fail to enable efficient removal of the gel at lower temperatures.